Electrically variable phase shifter



Feb. 1966 J. MUNUSHIAN ETAL 3,235,320

ELECTRICALLY VARIABLE PHASE SHIFTER Original Filed Jan. 4, 1960 3 Sheets-Sheet 1 604 7104 04 746! fol/z 6 5 Jiwzflmwsx/wM Zaaazr Adam/M,

Feb. 15, 1966 J. MUNUSHIAN ETAL 3,235,820

ELEQTRICALLY VARIABLE PHASE SHI'FTER Original Filed Jan. 4, 1960 3 Sheets-Sheet z 6y aw Feb. 15, 1966 J. MUNUSHIAN ETAL ELECTRICALLY VARIABLE PHASE SHIFTER Original Filed Jan. 4, 1960 3 Sheets-Sheet 5 United States Patent 3,235,820 ELECTRICALLY VARIABLE PHASE SHIFTER Jack Munushian, Los Angeles, Calif., and Robert H. Hardin, Littleton, Colo., assignors to Hughes Aircraft Company, Culver City, Calif, a corporation of Delaware Continuation of application Ser. No. 446, Jan. 4, 1960. This application Aug. 12, 1963, Ser. No. 301,576 4 Claims. (Cl. 333-31) The present invention relates to phase shifters and, more particularly, to apparatus for shifting the phase of a wave in which the amount of phase shift is controlled electrically.

This is a continuation of a prior copending application Serial No. 446, filed January 4, 1960, now abandoned.

In the past there have been numerous attempts to devise satisfactory means for shifting the phase of electromagnetic energy at ultra high or microwave frequencies. In one form of phase shifter, a section of waveguide is provided with a reflector such as movable Wall. Any energy incident upon the wall is reflected back along the waveguide. By mechanically moving this reflector axially along the waveguide, the distance over which the energy travels can be controlled. As a result, this in turn will control the phase of the reflected energy. Unfortunately, such systems are normally bulky and difficult to operate. Moreover, the inertia inherent in such a mechanical device limits the response time. In addition, as the wavelength of the energy decreases it becomes more ditficult to obtain the required accuracy from such a phase shifter without employing excessive precision in producing the parts.

In another form of phase shifter, the gyromagnetic resonance characteristics of a ferrite material are employed for shifting the phase. In such devices a ferrite member is disposed in the path of the electromagnetic energy so that the energy will travel therethrough. By creating a steady magnetic field in the ferrite material the resultant gyromagnetic effects will cause the phase of the energy to be changed. Such phase shifters have normally required an excessively long length of transmission line and/or excessively large magnetic fields to provide the required amount of phase shifting. Such a magnetic field requires a considerable amount of power to maintain. Also, as the frequency of the energy increases there are increased losses in the ferrite material.

It is therefore an object of the present invention to provide a phase shifting device which is free of mechanically moving parts and which provides a maximum amount of phase shift while consuming a minimum amount of power.

In accordance with this and other objects of the invention, electrically variable capacitance elements are employed to reflect incident energy with a phase angle that is a function of the capacitance thereof. The electrically variable capacitance elements are incorporated in a network of intercoupled Wave transmission elements which is arranged and adapted to provide solely reflected energy at an output terminal. In exemplary embodiments, the electrically controllable capacitance elements are reversebiased semiconductor devices or the like, and the network of intercoupled wave transmission elements is a ring hybrid bridge circuit, a waveguide short-slot hybrid coupler, a plurality of strip transmission lines intercoupled by suitable juxtaposition of the conductive strips, or the like.

The following specification and the accompanying drawings describe and illustrate exemplary embodimentsof the present invention. Consideration of the specification and the drawings will provide an understanding of the Patented Feb. 15, 1966 invention, including the novel features and objects thereof. Like reference characters denote like parts throughout the figures of the drawings.

FIG. 1 is a diagrammatic view of one embodiment of the present invention;

FIG. 2 is a cross-sectional view of a portion of the embodiment of FIG. 1;

FIG. 3 is a perspective view of another embodiment of the present invention;

FIG. 4 is a cross-sectional view of a portion of the embodiment in FIG. 3;

FIG. 5 is a plan view of a network of conductive strips for a phase shifter employing strip transmission line;

FIG. 6 is a cross-sectional view taken substantially along the lines of 6-6 in FIG. 5; and

FIG. 7 is a cross-sectional view of the terminal end of the network of FIG. 5.

Referring now to FIG. 1 of the drawings, the present invention is embodied in a phase shifter 10 adapted to be employed in an ultra high frequency or microwave system for interconnecting an input device 14 and an output device 16 so that electromagnetic energy may be coupled therebetween with a variable phase. The input device 14 may be of any desired variety from which electromagnetic energy of the desired frequency range is available. The output device 16 may be of any variety suitable for utilizing the electromagnetic energy that is supplied thereto.

The present phase shifter 10 includes a plurality of individual units 18, 20 and 22 that may be used separately or cascaded, as shown, so as to provide the desired range of phase shift. These units 18, 20, 22 which are preferably identical to each other may comprise hybrid rings, hybrid junctions, circulators, etc., employing any desired form of waveguiding means. In the present instance the first unit 18 comprises a hybrid ring 24 of coaxial transmission line wherein an outer conductor is disposed concentrically about an inner conductor and is spaced therefrom by a suitable dielectric medium.

The inner and outer conductors of the ring 24 are unbroken and free from any discontinuities so that electromagnetic energy may be propagated therearound in either direction with a minimum amount of loss.

The energy is supplied to the unit 18 by means of a coaxial cable 26 that has one end thereof connected to the input device 14. The other end of the cable 26 has the inner and outer conductors connected to the inner and outer conductors, respectively, of the ring 24. The energy is coupled out of the unit 18 by means of a coaxial cable 28 having its inner and outer conductors connected to the inner and outer conductors, respectively, of the ring 24 at a point located approximately one-third of the rings circumference from the point at which power is supplied to the ring 24.

The circumference of the ring 24 is preferably equal to approximately one and one-half electrical wavelengths at the frequency of the energy which is applied to the ring 24. Thus, from the input 26 to the output 28 in a clockwise direction around the ring 24 is one-half wavelength while in the counterclockwise direction the energy travels a full wavelength. Consequently, the portions of energy propagating by these two paths arrive at the output 28 degrees out of phase with each other. Thus there is a complete cancellation of the energy and no energy appears in the output cable 28 as a result of following such a direct route.

In addition to the input 26 and output 28, a pair of arms 30, 32 are connected to the ring 24 at predetermined locations. The first arm 30 comprises a section of coaxial cable that has the inner and outer conductors 34, 36 (see FIG. 2), connected to the inner and outer conductors, respectively, of the ring 24. The arm 30 extends outwardly from the ring for a distance equal to one-quarter wavelength plus a distance a. The arm 30 is preferably connected to the ring 24 midway between the input 26 and output 28 so as to be substantially onequarter of a wavelength from each. The outer end of the arm 30 is terminated by a variable reactance device 38. In the present instance the variable reactance device is a reversely biased semiconductor diode 40 which has a capacitance that varies as a function of the bias voltage thereacross.

The diode 40, as may be seen in FIG. 2, is mounted in a holder 42 that includes an outer conductive case 44. One end of this case 44 includes a flange 46 that is connected to a similar flange on the end of the outer conductor 36 of the arm 30. The interior of the case 44 registers with the inside of the outer conductor 36 and forms a continuation thereof. The diode 40 is disposed axially in the center of the passage and has the conductive lead 48 on one end connected to the center conductor 34 of the arm 30. The conductor 50 from the other end of the diode 40 extends through the center of a conductive end wall 52 so as to be connected thereto. The wall 52 is slidable within the case 44 so that it can be moved axially toward and away from the diode 40. A screw adjustment 54 is provided for controlling the movement and position of the wall 52 relative to the diode 40.

The center conductor 34 of the coaxial cable is connected to a control voltage source 56 by any suitable means. In the present instance a conductor 58 extends axially through the center of a half wave stub 60 and is connected to the center conductor 34 of the arm. It may be desirable to provide a choke 62 in the conductor 58 and a condenser 64 in the conductor 34 of the arm 30 to prevent loss of RF (radio frequency) energy to the voltage source and the leakage of DC. (direct current) into the system 12.

The position of the movable Wall 52 is adjusted relative to the diode 40 to tune the total reactance of the diode 40 and the section of coaxial line therebehind to resonate at approximately the center of the frequency range in which it is desired to operate. The capacitance of the diode 40 for. this tuning should be the capacitance at which the smallest amount of change in the bias voltage will produce the maximum amount of change of capacitance. It will be seen that when the movable wall 52 is properly adjusted, the diode 40 and wall 52 act as a tuned shorted half-wave stub. Consequently, the angle of the reflection coeflicient is substantially 180 degrees at the resonant frequency.

Any electromagnetic energy that leaves the ring 24 and enters the arm 30 is propagated radially outward along the arm 30 toward the end thereof. When the energy reaches the diode 40 and the short circuit provided by the wall 52 therebehind, the energy is reflected back along the arm 30 toward the ring 24. If the diode 40 has a high Q, i.e., the ratio of reactance to resistance is high, substantially complete reflection occurs and there is little or no loss of energy. The angle of the reflection coeflicient is a function of the voltage across the diode 40.

The second arm 32 is very similar to the first arm 30 in that it also comprises a section of coaxial cable that has the inner and outer conductors connected to the inner and outer conductors of the ring 24. The second arm 32 is connected to the ring 24 at a point substantially diametrically opposite to the input and has a length equal to a, i.e., it is one-quarter wavelength shorter than arm 30.

The outer end of the arm 32 is terminated by means of a second variable reactance device comprising a diode 66 substantially identical to the variable capacitance diode in the first arm 30. The diode 66 is mounted in a holder similar to the one illustrated in FIG. 2. The holder includes an adjustable wall and means for supplying a bias voltage to the diode 66. It may thus be seen that any energy traveling radially outward along the arm 32 is 4 reflected from the diode 66 and wall at the end of the arm 32 and the angle of the reflection coeflicient is a function of the capacitance of the diode 66 which in turn is a function of the bias voltage thereacross.

It may thus be seen that the energy applied to the input cable 26 enters the ring 24 where it divides into two portions that propagate around the ring 24 in opposite directions. The portion of energy traveling clockwise arrives at the output 28 with a one-half wavelength delay while the portion traveling counterclockwise arrives at the output 28 with a delay of one full wavelength. Consequently, the energy is one-half wavelength out of phase so as to cancel and prevent this unreflected energy from appearing at the output 28.

However, the portion of the energy propagating in a clockwise direction from the input 26 arrives at the first arm 30 with only one-quarter wavelength delay. The other portion of energy propagating in a counterclockwise direction is delayed by one and one-quarter wavelengths before arriving at the first arm 30. Consequently, both portions of the energy are in phase when they arrive at the first arm 30 and enter into the arm 30. Thus, energy is propagated radially outward toward the end of the arm 30.

The energy arriving at the second arm 32 is delayed by three-quarters of a wavelength irrespective of which direction it travels around the ring 24. Consequently, the energy enters the arm 32 and propagates radially outward toward the end Where it is reflected back toward the ring 24.

The energy that is reflected from the two diodes 40, 66 at the ends of the arms 30, 32 has a phase angle that may be varied by varying the bias across the diodes 40, 66. However, the energy that leaves the arms 30, 32 has a phase angle that is also determined by the length of the arms 30, 32.

As previously stated, the first arm 30 is one-quarter wavelength longer than the second arm 32. The energy thus experiences an additional delay of one-half wavelength in traversing the arm 30 in both directions. It may thus be seen that the energy that travels from the input 26 to the end of the first arm 30 and is reflected back into the ring 24 is returned to the input 26 with a delay of an integral wavelength (plus or minus the phase shift occurring at the point of reflection) irrespective of whether the energy travels in clockwise or counterclockwise directions. In addition, the energy that travels from the input 26 to the arm 32 so as to enter the second arm 32 and be reflected back to the input 26 is displaced by an odd multiple of half wavelengths (plus or minus the phase shift occurring at the point of reflection). This difference is a result of the one-quarter wavelength difference in the lengths of the arms 30, 32 and prevents any reflected energy being propagated back into the input 26, provided the coefficients of reflection are identical.

A similar analysis will show that the energy which is reflected from the diodes 40, 66 and is returned to the ring 24 will arrive in phase at the output 28 and is propagated through the output 28 if the coeflicients of reflection in the arms 30, 32 are identical. It may thus be seen that all of the energy that enters the ring 24 from the input 26 is reflected from the diodes 40, 66 and appears in the output 28. The phase of this energy may then be readily varied by merely varying the bias across the diodes 40, 66.

In the event a greater range of phase shifting is required than can be obtained from a single unit, a plurality of substantially identical units may be connected in series or cascaded. In the present instance the input 70 to the second unit 20 is connected to the output 28 of the first unit 18. This unit 20 includes a pair of variable capacitance diodes 72, 74, that are connected to the control voltage source 56. The output 76 thereof is in turn connected to the input 78 of a succeeding unit 22 that also includes a pair of variable capacitance diodes 78, 80 and has the output connected to the utilizing device 16.

Each of these units 18, 20, 22 thus provides a phase shift of the energy therein in response to the bias from the voltage source 56.

As an alternative, the embodiment of FIGS. 3 and 4 may be employed wherein the phase shifter 82 is particularly adapted for use in a microwave system that utilizes conventional rectangular Waveguide. The phase shifter 82 is contained in a hollow coupling unit 84 that defines a large rectangular chamber having one side thereof open. A septum or partition 86 extends longitudinally of the chamber so as to divide it into two separate compartments 88, 90 that are substantially identical to each other.

The outer end of the first compartment 88 is open to form an input 92 interconnected with a first section of waveguide 94- for receiving electromagnetic energy therefrom. The interior cross section of this chamber 88 is preferably substantially identical with the interior cross section of the waveguide 94. Thus, the energy flows from the waveguide 94 into the compartment 88 with no mismatching and/ or development of standing waves.

The inner end of the compartment 88 is terminated by a variable reactance semiconductor device or diode 108 and a conductive wall 98 that is disposed therebehind. The conductive lead 102 from one side of the diode 100 is connected to the coupling unit 84. The lead 106 from the other side of the diode 100 extends through a dielectric block 108 disposed in a wall of the coupling unit 84 so as to be electrically insulated therefrom. This lead 186 is connected to a suitable control voltage source 110 so that a reverse bias may be applied to the diode 100 and thereby control the capacitance thereof.

The wall 98 disposed behind the diode 100 preferably has a rectangular shape that fits the interior of the compartment 88 and forms a sliding fit therein. The wall 98 is secured to the end of a screw 112 that extends from the end of the coupling unit 84 so that the wall 98 may be moved axially of the compartment 88 toward and away from the diode 100. This permits the impedance terminating the compartment 88 to be tuned to resonate at the frequency employed. This impedance is preferably 50 tuned when the diode 180 is biased to a condition which provides the maximum variation of capacitance with a minimum change in bias. Thus, if the diode 100 and the wall 98 therebehind have a high Q, substantially complete reflection occurs and there is little or no loss of energy. Moreover, the angle of the reflection coefiicient is a function of the terminating capacitance which in turn is a function of the bias voltage across the diode 100.

The second compartment 98 is substantially identical to the first compartment 88. The outer end thereof is also open to form an output 112 that is interconnected with a second or output section of rectangular waveguide 114. The compartment 90 and waveguide 114 are preferably of the same size and shape so that the energy may flow from the compartment 90 into the waveguide section 114 with little or no mismatch whereby no standing waves or reflections occur.

The inner end of the compartment 90 includes a diode 116 that is mounted transversely of the narrow dimension of the compartment 90 substantially identical to the first diode 100. This diode 116 is disposed in a position corresponding to that of the first diode 100 and it is also connected to the control source 110. Thus, the capacitance of the diode 116 may be varied simultaneously and identically with that of the first diode 100. In addition, a movable wall 118 is mounted on a screw adjustment 120 so that the termination of the second chamber 90 may be tuned similar to the first chamber 88.

The partition 86 which separates the two compartments 88, 90 includes an aperture 122 that forms a short-slot hybrid or Riblet coupler which interconnects the two compartments 88, 90 with each other. The aperture 122 couples the energy from one compartment 88 into the other compartment 90. The energy which is thus coupled experiences a 90 degree shift in phase.

In operation, the energy propagated through the first section of waveguide 94 enters the input opening 92 and travels into the first chamber 88. When this energy arrives at the aperture 122, it divides into two substantially equal portions. One portion is coupled through the aperture into the second chamber 90. This energy is shifted degrees in phase and is propagated through the second chamber 90 toward the end thereof. The other portion continues on to the end of the first chamber 88. When this energy arrives at the end of the chamber 88 it is reflected from the diode and the wall 98 therebehind. The phase of the reflected energy is determined by the impedance of the termination. This, of course, is determined in part by the capacitance of the diode 100 which in turn is fixed by the bias voltage applied thereto by the voltage source 110.

The reflected energy is propagated back through the chamber 88 toward the input 92. When this energy arrives at the aperture 122 at least a portion thereof is coupled through the aperture 122 into the second chamber 90 with a 90 degree phase shift.

As previously stated, the portion of the energy that travels from the input 92 directly through the aperture 122 is shifted 90 degrees and is propagated toward the terminal end of the chamber 90. This energy is then reflected from the termination past the aperture 122. A portion thereof is coupled into the first chamber 88 with a phase shift of 90 degrees. Thus, if the angles of the coeflficients of reflection from the terminal ends of the two compartments 88, 90 are equal, the energy coupled back through the aperture 122 is 180 degrees out of phase with the energy remaining in the first chamber 88. As a result, there is a cancellation of these two portions of energy and no energy is reflected back into the first section of waveguide 94.

The energy that is reflected from the termination of the first chamber 88 and coupled through the aperture 122 is in phase with the energy that is reflected from the termination of the second chamber 90. Thus, all of the energy in the second chamber 90 is in phase and is propagated into the second section of waveguide 114.

It will thus be seen that all of the energy in the first section of waveguide 94 which is propagated through the input 92 into the phase shifter 82 is reflected from one or the other of the terminations at the inner ends of the chambers 88, 90 and is then discharged through the out put and into the second section of waveguide 114. Since this energy has been reflected from one or the other of the terminations it has a phase angle that is determined by the impedance of the terminations. Thus, since .the capacitances of the diodes 180, 116 are controlled by the voltage thereacross, the phase angle of the energy may be readily varied by regulating the output of the control voltage source 110.

As a further alternative, the embodiment of FIGS. 5, 6 and 7 may be employed. This phase shifter is particularly adapted for use in a microwave system utilizing so-called strip transmission line wherein electromagnetic energy is guided from one location to another by means of conductive strips that are disposed between a pair of conductive plates and separated therefrom by a dielectric material.

This phase shifter 130 includes a network 132 of center conductors that are mounted on a dielectric material 134 and are arranged between a pair of uniformly spaced conductive plates 136, 138.

The network 132 includes a first conductive strip which has one end thereof arranged to form an input 142 adapted to be connected to a source of electromagnetic energy. In addition, the conductor 140 also includes a substantially straight first coupling section 144 and a substantially straight second coupling section 146. The other end of the conductor 144 includes a termination 148 that causes microwave energy to be reflected therefrom.

The termination 148 includes a variable reactance device such as a variable capacitance diode 150 similar to those in the foregoing embodiments. The conductive lead 152 from one end of the diode is electrically connected to an end wall 154 formed by the outer conductors 136, 138. The conductive lead 156 from the other end of the diode 150 is coupled to the end of the center con ductor 148 by a condenser 158 so as to prevent the loss of DC. into the rest of the system. The lead 156 is also connected to a variable voltage source 160 by a choke 162 which prevents the loss of RF energy from the microwave system. It may thus be seen that energy arriving at the end of the center conductor 140 is reflected from the diode 150 and the angle of the coefiicient of reflection is a function of the capacitance of the diode 150.

A second conductor 164 is provided which includes a straight portion 166 that is juxtaposed to the coupling section 144 of the first conductor 140. These two sections 144, 166 are sufficiently close to each other to cause approximately one-half of the energy traveling from the input 142 toward the termination 148 of the conductor 140 to be coupled into the second conductor 164. The half of the energy remaining in the first conductor 140 continues along the conductor 140 toward the second coupling section 146.

A third conductor 168 is provided which includes a coupling section 170 that is closely spaced to the second coupling section 146. These two sections 146 and 170 are juxtaposed so that approximately half of the energy remaining in the first conductor 140 is coupled into the third conductor 168 and the rest remains in the first conductor 140. One end of the third conductor 168 is terminated in a variable capacitance diode 172. The diode 172 is similar to the diode 150 and is connected to the voltage source 160 in the same manner. The other end of the conductor 168 is terminated with a short circuit.

The second conduct-or 164 includes a second substantially straight coupling section 174 which is juxtaposed to a coupling section 176 in a fourth conductor 178 so that substantially one-half of the energy in the second conductor 164 is coupled into the fourth conductor 178. The end of the second conductor 164 is terminated in a variable capacitance diode 180. This diode 180 is mounted similar to diode 150 and is biased by the source 160 to control the capacitance thereof.

The fourth conductor 178 is substantially identical to the third conductor 168 in that one end thereof is terminated by a variable capacitance diode 182 and the other end is terminated with a short circuit.

In operation, microwave energy is supplied to the input- 142 of the first conductor 140 so that it is propagated therealong. As this energy is propagated across the first coupling portion 144, approximately one-half of the energy is coupled into the second conductor 166 while the remaining one-half of the energy continues to follow the first conductor 144. When this energy arrives at the second coupling section 146, half of the remaining energy, i.e., one-quarter of the input energy, is coupled into the third conductor 168 and a corresponding portion continues on to the termination of the first conductor 140 where it is reflected from the diode 150.

The energy in the third conductor 168 is reflected from the diode 172 at the end thereof and is coupled back into the first conductor 140. The lengths of the conductors 140, 168 and couplers are such that the energy reflected from the diodes 150, 172 cancels except the energy which is being propagated back along the first conductor 140.

The energy in the second conductor 166 is divided at the coupling sections 174, 176 so that the energy is reflected from the diodes 180, 182 and is propagated back along the second conductor 164. The lengths of the conductors 140, 166, 168, 178 are such that the various portions of the energy reflected from the diodes 150, 172, 180, 182 are all in phase at the output 184 and, accordingly, may be coupled from the output to a utilizing device. The energy that would otherwise be coupled from the second conductor 164 back to the first conductor would be out of phase with the energy remaining in the first conductor and would cause cancellation of the energy. Thus, none of the reflected energy appears at the input 142.

It may be seen that all of the energy that arrives at the output 184 has been reflected from one or the other of the four diodes 172, 180, 182. Thus, the phase of the energy at the output 184 is a function of the angles of the coeflicients of reflection from the various diodes. This in turn is a function of the capacitances of the diodes. Thus the control voltage source is effective to bias the diodes so as to provide the desired capacitances and therefore the desired phase shift. It should be noted that since the energy is reflected equally from four separate diodes, the amount of power that may be phase shifted is four times the amount of power that an individual diode can safely handle.

Thus, there has been described several embodiments of an electrically variable phase shifter which is free of mechanically moving parts and which provides a maximum amount of phase shift while consuming a minimum amount of power by utilizing electrically variable capacitance elements incorporated in a network of intercoupled wave transmission elements. In this manner applied input energy is reflected from the capacitance elements with a phase angle that is a function of the capacitance thereof and appears at the output terminal.

Although several embodiments of the invention have been shown and described, other variations may be made and it is intended that the foregoing disclosure is to be considered only as illustrative of the principles of the invention and not construed in a limiting sense.

What is claimed is:

1. An electrically variable phase shifter comprising:

(a) a hybrid bridge circuit having an input terminal, an output terminal, and a pair of wave transmission arms;

(b) a source of input wave energy coupled to said input terminal to provide points of maximum and minimum input energy in said hybrid bridge circuit, said wave transmission arms being at diiferent points of maximum input energy, said output terminal being at a point of minimum input energy;

(0) electrically controllable capacitive reactance means terminating ends of said wave transmission arms for providing reflected energy in said hybrid bridge circuit, the phase of said reflected energy with respect to said input energy being a function of the reactance of said electrically controllable capacitive reactance means;

(d) means disposed in one of said wave transmission arms to provide an additional 90 phase delay to energy propagated in either direction therein (with respect to the other of said wave transmission arms to provide a point of minimum reflected energy at said input terminal and a point of maximum reflected energy at said output terminal;

(e) and electrical control means coupled to said electrically variable capacitive reactance means for controlling the phase of said reflected energy.

2. An electrically variable phase shifter comprising:

(a) a ring hybrid bridge circuit including a ring portion and an input member, an output member, and a pair of phase control members connected to said ring portion;

(b) said phase control members being connected to said ring portion at separate points where energy applied at said input member and traveling in opposite directions around said ring portion arrives in phase;

(c) electrically variable capacitive reactance means for reflecting incident energy disposed at the ends of said phase control members remote from said ring portion;

(d) one of said phase control members being A wavelength longer than the other of said phase control members to provide cancellation of reflected energy at said input member;

(e) said output member being connected to said ring portion at a point where energy applied at said input member cancels and Where energy reflected from said phase control members is in phase for coupling solely reflected energy out of said ring portion;

(f) and electrical control means coupled to said electrically variable capacitive reactance means for equal- 1y varying the reactance thereof to cause equal variation of the coefficient of reflection of said phase control members.

3. An electrically variable phase shifter comprising:

(a) a ring hybrid bridge circuit including a ring portion and an input member, an output member, and first and second phase control members connected to said ring portion;

(b) said ring portion being an odd number of half wavelengths in circumference;

(c) said output member being connected to said ring portion at a point where energy from said input member traveling in opposite directions around said ring portion arrives out of phase and cancels;

((1) said phase control members being connected to said ring portion at separate points where energy from said input member traveling in opposite directions around said ring portion arrives in phase;

(e) electrically variable capacitive reactance means terminating the ends of said phase control members remote from said ring portion for causing reflection of energy entering said phase control members, said variable capacitive reactance means providing equal reactances to cause equal coeflicients of reflection in said phase control members;

(f) said second phase control member being A wavelength longer than said first phase control member for causing energy reflected into said ring portion by said second phase control member to be out of phase at said input member and in phase at said output member with respect to energy reflected by said first phase control member, whereby reflected energy ente-rs said output member;

(g) and electrical control means coupled to said electrically variable capacitive reactance means for equally varying the reactance thereof to cause equal variation of the coeflicient of reflection of said phase con trol members, whereby the phase of the energy in said output member is varied with respect to the phase of the energy in said input member,

4. An electrically variable phase shifter comprising:

(a) a ring hybrid bridge circuit formed of coaxial transmission line having a center conductor and an outer conductor, said ring hybrid bridge circuit including a ring portion and an input line, an output line, and first and second phase control lines connected to said ring portion;

(b) said ring portion being 1% wavelengths in circumference;

(c) said output line being connected to said ring portion a distance of /2 wavelength around said ring portion from the connection of said input line to said ring portion;

(d) said first phase control line being connected to said ring portion a distance of wavelength around said ring portion from the connection of said input line to said ring portion;

(c) said second phase control line being connected to said ring portion at a point wavelength distant from the connections of said input and output lines;

(f) said second phase control line being wavelength longer than said first phase control line;

g) mechanically movable short circuit means terminating the ends of said phase control lines remote from said ring portion;

(h) electrically variable capacitive reactance means disposed at the ends of said phase control lines remote from said ring portion and connected in series between the center conductor and said mechanically movable short circuit means;

(i) and electrical control means coupled to said electrically variable capacitive reactance means for controlling the reactance thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,834,876 5/1958 Pritchard 33331 2,854,645 9/1958 Arditi 333-97 2,874,276 2/1959 Dukes 33384 2,905,902 9/ 1959 Strandberg 3333l 2,908,813 10/1959 Morrison 33331 2,914,671 11/1959 De Lange 333-11 2,962,7 16 11/ 1960 Englemann 343--720 3,051,844 8/1962 Beam et al. 307-88.5

OTHER REFERENCES Uhlir: Proc. IRE, vol. 46, pages 1099-1115, June 1958.

HERMAN KARL SAALBACH, Primary Examiner. 

1. AN ELECTRICALLY VARIABLE PHASE SHIFTER COMPRISING: (A) A HYBRID BRIDGE CIRCUIT HAVING AN INPUT TERMINAL, AN OUTPUT TERMINAL, AND A PAIR OF WAVE TRANSMISSION ARMS; (B) A SOURCE OF INPUT WAVE ENERGY COUPLED TO SAID INPUT TERMINAL TO PROVIDE POINTS OF MAXIMUM AND MINIMUM INPUT ENERGY IN SAID HYBRID BRIDGE CIRCUIT, SAID WAVE TRANSMISSION ARMS BEING AT DIFFERENT POINTS OF MAXIMUM INPUT ENERGY, SAID OUTPUT TERMINAL BEING AT A POINT OF MINIMUM INPUT ENERGY; (C) ELECTRICALLY CONTROLLABLE CAPACITIVE REACTANCE MEANS TERMINATING ENDS OF SAID WAVE TRANSMISSION ARMS FOR PROVIDING REFLECTED ENERGY IN SAID HYBRID BRIDGE CIRCUIT, THE PHASE OF SAID REFLECTED ENERGY WITH RESPECT TO SAID INPUT ENERGY BEING A FUNCTION OF THE REACTANCE OF SAID ELECTRICALLY CONTROLLABLE CAPACITIVE REACTANCE MEANS; 